1. Field of the Invention
This invention relates to a spandex fiber which has increased resistance to discoloration caused by exposure to fumes. In particular, the invention concerns a polyether-based spandex fiber to which improved resistance to nitrogen dioxide is imparted by a saturated aliphatic polyester additive.
2. Description of the Prior Art
Spandex fibers are well known in the art. The fibers are formed from long chain synthetic polymer comprising at least 85% segmented polyurethane. Spandex fibers made from polyether-based polyurethane polymers are known to discolor upon prolonged exposure to fumes, especially nitrogen dioxide, which is an important constituent of combustion gases and atmospheric smog. Many agents have been suggested for increasing the resistance of polyether-based spandex fibers to such fume-induced discoloration. Among these many agents are those of Japanese Patent Application Publication No. (Sho) 49-35812 which discloses a polyether-based polyurethane that is stabilized against fume-induced discoloration by having dispersed within the fiber a monoester compound which is the reaction product of a saturated higher fatty acid and a saturated higher fatty alcohol, the acid and the alcohol each having between 12 and 18 carbon atoms. Monoesters such as tridecyl laurate, stearyl laurate, dodecyl stearate and hexadecyl palmitate are specifically exemplified. However, such monoesters of the art, as is shown in Example IV below, are much inferior to the polyester additives used in accordance with the present invention for increasing the resistance of polyether-based spandex fibers to fume-induced discoloration. Furthermore, the monoester additives of the art often can be removed from the fibers by ordinary scouring procedures commonly used in fabric manufacture.
From a practical standpoint, some discoloration of the fiber can be tolerated without it being noticed by users of fabrics made with polyether-based spandex fibers. Nonetheless, the utility of the fibers would be enhanced by improvements in the resistance of the fibers to fume-induced discoloration. It is an object of this invention to provide such an improvement.